Method and device for coating a product

ABSTRACT

A method includes coating a product with a metallic coating, in particular a high-temperature component product of a gas turbine, in a vacuum plant. An apparatus coats the product with a metallic coating in a vacuum plant, having a coating chamber and a postheat treatment chamber. Novel process control with regard to a temperature profile, in particular after the application of the metallic coating to the product and before the postheat treatment, involves the ensuring of a minimum temperature at all times, this minimum temperature being relatively higher than room temperature.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/EP00/01301 which has an Internationalfiling date of Feb. 17, 2000, which designated the United States ofAmerica, the entire contents of which are hereby incorporated byreference.

FIELD OF THE INVENTION

The invention relates to a method of coating a product with a metalliccoating, in particular with a metallic anti-oxidation coating, in avacuum plant. In the method, the product is fed into the vacuum plantand heated from room temperature to a product temperature, the metalliccoating is applied to the product, and the coated product is subjectedto a postheat treatment. Furthermore, the invention relates to anapparatus for coating a product with a metallic coating in a vacuumplant, the vacuum plant including a coating chamber and a postheattreatment chamber.

BACKGROUND OF THE INVENTION

Coating plants for coating gas turbine blades are known, e.g. an inlineEB-PVD coating plant from Interturbine Von Ardenne GmbH (EB-PVD:Electron Beam—Physical Vapor Deposition), in which a ceramic coating isapplied to the gas turbine blade by means of physical vaporizationprocesses. Such a coating plant, for example, may be composed ofchambers arranged directly one behind the other and connected to atransfer system for conveying the turbine blades. In this case, thefirst chamber serves as a loading chamber for turbine blades. From theloading chamber, the turbine blades are transported into a second vacuumchamber connected to the loading chamber and are preheated there.Further transport into a process chamber then takes place, in whichprocess chamber a ceramic material, in particular an yttrium-stabilizedzirconium oxide, is heated, melted and vaporized by means of electronbeam vaporization. The ceramic material condenses on the turbine bladesand therefore forms the ceramic coating. The turbine blades thus coatedare transported further into a cooling chamber and cooled therein. Thecooling is effected without monitoring, in particular in an uncontrolledmanner, since the turbine blades are left on their own in the coolingchamber and consequently emit their heat to the surroundings via heatradiation until they have cooled down to room temperature.

U.S. Pat. No. 5,238,752 discloses a heat-insulating-coating system whichis applied to a turbine blade. In this case, the parent material of theturbine blade consists of a nickel-base superalloy to which a metallicprotective or bonding coating of the type MCrAlY or PtAl is applied.Here, M stands for nickel and/or cobalt, Cr stands for chromium, Alstands for aluminum, Y stands for yttrium and Pt stands for platinum.Forming on this metallic bonding coating is a thin coating of aluminumoxide, to which the actual ceramic heat-insulating coating of zirconiumoxide stabilized with yttrium is applied. In this case, the turbineblade is coated by means of a physical vaporization process in which theceramic material (zirconium oxide) is vaporized by being bombarded withelectron beams. This coating process is effected in a vacuum chamber,the turbine blade being heated via a substrate heater by means of heatradiation to a temperature of about 1200 K to 1400 K, in particularabout 1300 K.

Those coatings on turbine blades which are produced in theabove-described, known methods and apparatuses are still capable ofimprovement with regard to their service life, in particular in the caseof hot-gas admission when used in a gas turbine.

SUMMARY OF THE INVENTION

The object of the invention is to provide a method of coating a productwith a metallic coating. In this case, the fatigue strength of themetallic coating, in particular against corrosive and oxidizing attacks,is to be markedly improved. A further object of the invention is tospecify an apparatus for coating a product with a metallic coating. Theproduction of a metallic coating of high quality on the product is to bepossible with the apparatus.

According to the invention, the first-mentioned object is achieved by amethod of coating a product with a metallic coating, in particular witha metallic anti-oxidation coating, in a vacuum plant. In this method,the product is fed into the vacuum plant and heated from roomtemperature to a product temperature; the metallic coating is applied tothe product; and the coated product is subjected to a postheattreatment. The postheat treatment follows the application of the coatingin such a way that the temperature of the product after the applicationof the coating and before the postheat treatment is at least as high asa minimum temperature, the minimum temperature being relatively higherthan room temperature.

In this case, the invention is based on the idea that the quality of aprimary metallic coating applied to the parent material of a product isespecially important. Material properties and characteristic coatingproperties, such as the homogeneity of the coating, the bonding to thesubstrate, and the structure of the boundary layer between coating andsubstrate for example, are important quality features. These also havean effect on the bonding and condition of further coatings which areapplied to the primary coating possibly in further coating processes.

A metallic coating on a product, for example a metallic anti-oxidationcoating, will therefore develop its function more effectively, forinstance as a protective coating against corrosion and/or oxidation, thebetter the abovementioned coating properties are realized. For theservice life of metallic coatings on products which appear underoxidizing or corrosive conditions, for example, in addition to theselection of the materials, in particular the bonding of the coating tothe parent material of the product is decisive. This depends on thetreatment of the product in all the phases of the production process. Inthis case, chemical and physical—in particular thermal—influences whichmay possibly impair the forming and bonding of the coating are to betaken into account.

Chemical influences can be largely reduced by the selection of suitablematerials for all the built-in components of the equipment, which as faras possible are to be chemically inert with respect to the coatingmaterials. Physical conditions under which the process for producing acoating takes place relate to the process control in its entirety, thatis to say from the preparation of the product, via the application ofthe protective coating up to the further treatment of the product,normally a subsequent postheat treatment—and all possible intermediatesteps.

The monitoring and configuration of the process control in all thephases of the production process is therefore very important. In thiscase, time-dependent and locus-dependent thermodynamic processparameters, such as pressure and temperature, to which the product issubjected in the production process are to be taken into account. Forexample, on account of the generally different coefficients of thermalexpansion of parent material and coating material, the producttemperature during the application of the coating (coating temperature)and the temperature profile up to completion of a postheat treatment ofthe coated product have a considerable effect on the formation of theboundary layer between product surface and coating.

Virtually steady process control with regard to the temperature in allthe phases of the process for producing the metallic coating can beachieved with the method. In this case, after the application of themetallic coating to the product and before the postheat treatment, aminimum temperature of the product is ensured at all times, this minimumtemperature being higher than room temperature.

In the case of products which constitute high-temperature components ofgas turbines, for instance in the case of gas turbine blades or heatshield elements of combustion chambers, this minimum temperature ispreferably about 500 K, in particular about 900 K to 1400 K.

The method operates on a product that is always close to a state ofthermodynamic equilibrium with its surroundings. Time-dependent andspatial temperature gradients, in particular thermal shocks, areavoided. By this novel method in the process control with regard to thetemperature profile, it is possible to markedly improve the bonding ofthe metallic coating to the parent material of the product in thepostheat treatment. In the postheat treatment following the applicationof the metallic coating in this manner, a firm connection between parentmaterial and coating material is produced by diffusion actions, and acoating of high quality is formed on the product.

The application of the metallic coating to the product is preferablyeffected in a coating region and the postheat treatment is preferablyeffected in a postheat treatment region. In this case, the coatingregion and the postheat treatment region are different regions of thevacuum plant. It is advantageous to carry out the application of themetallic coating to the product and the postheat treatment in the samevacuum plant but spatially separate from one another, since theseprocess steps are carried out at somewhat different temperatures andgenerally have different process times. For example, the application ofa metallic coating to a gas turbine blade, in particular a metallicanti-oxidation and anti-corrosion coating, is carried out at a coatingtemperature of about 1100 K to 1200 K, whereas the postheat treatment ofthe gas turbine blade is effected at a postheat treatment temperature ofabout 1200 K to 1500 K. The separation of coating region and postheattreatment region has a favorable effect on the quality andreproducibility of the metallic coatings. A situation in which differentprocess steps having different process parameters are carried out in thesame region of a plant is avoided. This could be effected virtually onlywith a periodic change of the operating parameters of the vacuum plant,a factor which impairs the quality and reproducibility of the coatings.

The coated product is preferably transferred automatically from thecoating region into the postheat treatment region. This procedure isvery advantageous with regard to industrial production of the metalliccoating. In particular in a vacuum plant, automatic, preferablyelectronically controlled, transfer of the products is far superior toother known embodiments, for example with complicated manipulatorsmanually operable externally and with sealed vacuum leadthroughs.

The product subjected to postheat treatment is preferably cooled down toroom temperature in a controlled manner. The cooling to room temperatureis also preferably carried out in a controlled or regulated manner. Thisis effected just prior to possible removal of the product from thevacuum plant. Monitoring and control of the cooling operation avoids asituation in which, after completion of the postheat treatment, theproduct is cooled down in an uncontrolled manner to room temperature, afactor which could have an adverse effect on the coating properties onaccount of the thermal stresses which then occur between the metalliccoating and the substrate.

A first number of products is preferably located in the coating regionand simultaneously a second number of products is preferably located inthe postheat treatment region, the second number being larger than thefirst number. This procedure is very advantageous with regard toindustrial series production of metallic coatings on products. Themetallic coating is applied to products in the coating region, while atthe same time products are subjected to a postheat treatment in thepostheat treatment region. This provides for efficient production ofmetallic coatings on products. A continuous and simultaneous pass ofproducts through the method steps is possible.

In particular, in this continuous method, the pass of products per unitof time is markedly increased compared with non-simultaneous methodsteps. In the method, due to the different process times of theindividual method steps, more products are subjected to a postheattreatment than are located at the same time in the coating region, sincethe postheat treatment process generally constitutes the limitingprocess with respect to time. For example, the application of a metalliccoating to a gas turbine blade, in particular the application of ametallic anti-oxidation and anti-corrosion coating, has a process timeof about 30 min, whereas the postheat treatment of the gas turbineblade, at about 60 min to 240 min, lasts considerably longer. Bydesigning the vacuum plant with due regard to the respective processtimes, a continuous and simultaneous pass of products is ensured, andefficient production is made possible.

The product used is preferably a high-temperature component of a gasturbine, in particular a gas turbine blade or a heat shield element of acombustion chamber. Furthermore, the parent material used for thehigh-temperature component is preferably a nickel- or iron- orcobalt-base superalloy. A gas turbine blade is a high-temperaturecomponent which is arranged in the hot-gas duct of a gas turbine. Adistinction is made between turbine guide blades and turbine movingblades, which are exposed to high thermal loads, in particular in gasturbines having high turbine inlet temperatures of over 1500 K forexample, and to corrosive and oxidizing conditions due to the hot gas.Therefore an appropriate alloy has to be selected for the parentmaterial. An example of a high-temperature-resistant alloy of this typewith high creep strength on a nickel basis is Inconel 713 C, which inits essential components is produced from 73% nickel, 13% chromium, 4.2%molybdenum and 2% niobium.

The metallic coating used is preferably an MCrAlX alloy, where M standsfor one or more elements of the group comprising iron, cobalt andnickel, Cr stands for chromium, Al stands for aluminum, and X stands forone or more elements of the group comprising yttrium, rhenium and theelements of the rare earths. This metallic coating is applied to theproduct, in particular the high-temperature component of a gas turbine,in the coating region in a known manner by thermal spraying with the VPS(Vacuum Plasma Spraying) or LPPS (Low Pressure Plasma Spraying)processes. The MCrAlX coatings are especially suitable forhigh-temperature components in gas turbines having a parent material ofa nickel-, or iron- or cobalt-base superalloy. They are suitable instationary gas turbines and aircraft engines having a high turbine inlettemperature. In addition, they are suitable as an adhesive mediatorcoating for the application of further coatings in other coatingprocesses, such as, for example, for producing a ceramic heat-insulatingcoating on a product by means of PVD (Physical Vapor Deposition).

The object which relates to the apparatus is achieved according to theinvention by an apparatus for coating a product with a metallic coatingin a vacuum plant, comprising a coating chamber and a postheat treatmentchamber, the postheat treatment chamber being connected to the coatingchamber in a vacuum-tight manner.

This makes it possible for the application of the metallic coating to aproduct and the subsequent postheat treatment to be carried out in oneplant. The vacuum-tight connection between the coating chamber and thepostheat treatment chamber ensures that the product is at no timeexposed to the atmosphere, in particular the oxygen in the air, duringthe method. The vacuum plant is therefore superior to conventionalplants in which separate vacuum chambers which are not connected to oneanother in a vacuum-tight manner are provided for the application of thecoating and for the postheat treatment.

A heating device is preferably provided in the postheat treatmentchamber. The heating device is realized in known configurations, forexample by a radiant heating element for indirect radiant heating or byan electron beam gun for heating the product by direct electronbombardment. For the postheat treatment, the process control is to beconfigured with regard to the temperature of the product in such a waythat the product temperature is set at a predetermined value, thepostheat treatment temperature. In this case, the postheat treatmenttemperature is set by measuring the temperature of the product andregulating the heating output of the heating device, for example byregulating the radiation output of a radiant heating element via theheating current.

A preheating chamber is preferably provided, this preheating chamberbeing arranged upstream of the coating chamber and being connected tothe latter in a vacuum-tight manner. The preheating chamber is designedas a vacuum chamber and is an integral part of the entire vacuum plantfor coating a product with a metallic coating. Provided in thepreheating chamber is a heating device which is designed in a knownmanner, for example by a radiant heating element for indirect radiantheating or by an electron beam gun for heating the product by directelectron bombardment. The preheating chamber serves, on the one hand, toreceive and preheat the product from room temperature to a producttemperature and, on the other hand, to pretreat and prepare the productfor subsequent method steps, in particular for the application of themetallic coating to the product in the coating chamber. In thepreheating chamber, possible impurities which may have entered thesurface of the product can also be emitted as gases from the product.Impurities may adversely affect the application of the coating to theproduct and thus the quality of the coating. Therefore the preheatingchamber, in addition to the preliminary process heating, at the sametime performs an important cleaning function for the product to becoated, so that, due to the degassing process, a product having anappropriately clean prepared surface and well-defined producttemperature is prepared.

A cooling chamber is preferably provided, this cooling chamber beingarranged downstream of the postheat treatment chamber and beingconnected to the latter in a vacuum-tight manner. A product is heatedafter it has been subjected to the postheat treatment. In order to treatthe product further or feed it to its destination, it is brought to roomtemperature in a suitable manner. To this end, it has to be cooled down,for which purpose, in conventional methods, the external postheattreatment chamber, which is not coupled to a coating chamber, islikewise used. The product is cooled down in a controlled manner in thispostheat treatment chamber.

In the vacuum plant, on the other hand, the controlled cooling operationis effected in a separate cooling chamber. In this case, the coolingchamber is designed as a vacuum chamber and is an integral part of theentire vacuum plant. In order to cool the product in a controlledmanner, a heating device is provided in the cooling chamber. Thisheating device ensures that the product is at a predeterminedtemperature during the cooling operation. As a result, the product isnot cooled too rapidly via heat radiation or heat conduction to thesurroundings but is cooled virtually steadily by the temperature beingreduced down to room temperature gradually and in a controlled manner byregulating the heating output of the heating device.

The heating device is designed, for example, in the form of a knownradiant heating element for indirect radiant heating of the product.Additional known treatment devices for cooling the product, for instancein the form of a gas supply system for inert cooling gases (e.g. argon),can be provided in the cooling chamber. In this embodiment, inertcooling gas is admitted in a carefully metered manner to the heatedproducts and the latter are cooled down to room temperature in acontrolled manner. The cooling chamber advantageously serves at the sametime as a removal chamber for the products.

The vacuum-tight connection between the coating chamber and the postheattreatment chamber is preferably produced via a lock chamber. Both theprocess times for the application of the metallic coating to the productand for its postheat treatment and the respective process parameters, inparticular the coating temperature and the postheat treatmenttemperature, are different. For example, the application of a metalliccoating to a gas turbine blade, in particular a metallic anti-oxidationand anti-corrosion coating, is effected at a coating temperature ofabout 1100 K to 1200 K. On the other hand, the postheat treatment of thecoated gas turbine blade is effected at a markedly higher postheattreatment temperature of 1200 K to 1500 K.

It is therefore expedient to also spatially separate these processesfrom one another by appropriate devices, here realized by a separatelock chamber, to such an extent that mutual interactions are largelyruled out. This configuration is also favorable in terms of the method.In this case, the lock chamber serves primarily to transfer the productsfrom the coating chamber to the postheat treatment chamber. It is anintegral part of the vacuum plant. A heating device is preferablyprovided in the lock chamber, this heating device ensuring apredetermined product temperature during the transfer.

In this case, the product temperature in the lock chamber canadvantageously be continuously adapted to the respective processtemperatures during the transfer of the products from the coatingchamber into the postheat treatment chamber. Furthermore, when thevacuum plant is used for industrial series production in a simultaneouscontinuous method, the lock chamber serves as an important buffer systemin order to adapt the quantities to one another, if need be, and thusensure as far as possible a continuous pass of products.

A transfer system is preferably provided for the automatic transfer ofthe product from a vacuum chamber (preheating chamber, coating chamber,lock chamber, postheat treatment chamber, cooling chamber) into anothervacuum chamber of the vacuum plant

In particular in a vacuum plant, automatic, preferably electronicallycontrolled, transfer of the products is far superior to other knownembodiments, for example with complicated manipulators manually operableexternally and with sealed vacuum leadthroughs. In order to permit inparticular a continuous and automated pass of the products, the vacuumchambers of the vacuum plant (preheating chamber, coating chamber, lockchamber, postheat treatment chamber, cooling chamber) are equipped witha suitable transfer system. In this case, the transfer system hasdevices for receiving products, for transporting products and fortransferring products, the devices being arranged in the individualvacuum chambers.

The coating chamber preferably has a first receiving capacity and thepostheat treatment chamber preferably has a second receiving capacityfor products, the second receiving capacity being greater than the firstreceiving capacity. In general, the (average) number of products in avacuum chamber is obtained from the number of fed products per unit oftime multiplied by the (average) retention time of the products in thevacuum chamber.

In the ideal continuous pass, the number of fed products per unit oftime is the same for all vacuum chambers. The (average) number ofproducts in a vacuum chamber is then determined by the retention time inthis vacuum chamber. The relative receiving capacities to be planned forproducts for the coating chamber and for the postheat treatment chamberare then approximately given by the respective process times in thesevacuum chambers.

For the application of an MCrAlX coating according to the VPS or LPPSprocess to a gas turbine blade having a parent material made of anickel-, iron- or cobalt-base superalloy, a process time of typicallyabout 30 minutes is obtained, whereas the postheat treatment of the gasturbine blade has a process time of about 120 minutes. The postheattreatment chamber is therefore to be dimensioned and configured in sucha way that its receiving capacity for gas turbine blades is at leastfour times as great as the receiving capacity of the coating chamber.The vacuum plant is conceived in such a way that it advantageouslypermits an adaptation of the receiving capacities to the respectiveprocess times and thus a continuous and simultaneous pass of products, afactor which in turn is very favorable for industrial series production.

BRIEF DESCRIPTION OF THE DRAWINGS

The apparatus and the method for coating a product with a metalliccoating in a vacuum plant are explained in more detail by way of examplewith reference to the non-limiting exemplary embodiments discussed inthe application and shown in the drawings, in which, in a partlyschematic and simplified manner:

FIG. 1 illustrates a schematic longitudinal section of a vacuum plantfor coating products, for example gas turbine blades, with a metalliccoating,

FIG. 2 is a diagram with a simplified temperature profile for a productaccording to a conventional method, and

FIG. 3 is a diagram with a simplified temperature profile for a productaccording to the method according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A vacuum plant 1 for coating products 12, here gas turbine blades 12 forexample, with a metallic coating 13 is shown schematically in FIG. 1 ina longitudinal section. The vacuum plant 1 has various vacuum chambers2, 3, 4, 5, 6—successively a preheating chamber 2, a coating chamber 3,a lock chamber 4, a postheat treatment chamber 5 and a cooling chamber6. In this case, the coating chamber 3 is connected in a vacuum-tightmanner to the postheat treatment chamber 5 via the lock chamber 4. Thepreheating chamber 2 is arranged upstream of the coating chamber 3 andis connected to the latter in a vacuum-tight manner. The cooling chamber6 is arranged downstream of the postheat treatment chamber 5 and isconnected to the latter in a vacuum-tight manner.

In each case, at least one heating device 7, 7A is provided in thepreheating chamber 2, the lock chamber 4, the postheat treatment chamber5 and the cooling chamber 6. In the exemplary embodiment shown, theheating devices 7, 7A in the individual vacuum chambers 2, 4, 5, 6 aredesigned as radiant heating elements for the controlled heating of thegas turbine blades 12 arranged in the vacuum chambers to a predeterminedproduct temperature. Provided in the vacuum chambers 2, 3, 4, 5, 6 is atransfer system 8, 11 which is designed in each case as adelivery/receiving device 11 and transport device 8 in the individualvacuum chambers 2, 3, 4, 5, 6. In each case at least two gas turbineblades 12 are arranged on the respective transport devices 8 in thepreheating chamber 2, the lock chamber 4, the postheat treatment chamber5 and the cooling chamber 6.

The coating chamber 3 has a coating region 9 in which a coating device14 and a holder 16, rotatable about a longitudinal axis 17, for gasturbine blades 12 are arranged. In this case, the coating device 14 isdesigned as a VPS (Vacuum Plasma Spraying) or LPPS (Low Pressure PlasmaSpraying) device (plasma torch) for the thermal spraying of coatingmaterial 15—for example MCrAlX—onto a gas turbine blade 12. The coatingdevice 14 at the same time serves to heat the gas turbine blade 12 to apredetermined product temperature. This is ensured during a coatingoperation by the hot process gases of the coating device 14 (plasmatorch) and by the coating material 15 striking the gas turbine blade 12.

A gas turbine blade 12 is located in the coating region 9 on the holder16. The coating device 14 is arranged above the gas turbine blade 12 inthe coating region 9. Formed in the postheat treatment chamber 5 is apostheat treatment region 10, in which a number of coated gas turbineblades 12 having a metallic coating 13, in particular an MCrAlX coating,are located on the transport device 8. In this case, the number of gasturbine blades 12 in the postheat treatment region 10 is greater thanthe number of gas turbine blades 12 in the coating region 9.

Two heating devices 7A are provided in the postheat treatment region 10.One heating device 7A is arranged above and the other heating device 7Ais arranged below the gas turbine blades 12, so that heating of the gasturbine blades 12 to a predetermined product temperature (which is thepostheat treatment temperature) is thereby ensured by heat radiation.The vacuum chambers 2, 3, 4, 5, 6 of the vacuum plant 1 are connected toa vacuum pump system (not shown in FIG. 1), which preferably consists ofa diffusion pump, valves and vacuum measuring devices and also a backingpump, so that a respectively required vacuum can be set in theindividual vacuum chambers 2, 3, 4, 5, 6.

In the coating method for coating a product 12, for example a gasturbine blade 12, with a metallic coating 13, a metallic MCrAlXanti-oxidation coating, in a vacuum plant 1, a gas turbine blade 12 isfirst of all fed into the preheating chamber 2 and arranged on thetransport device 8 of the transfer system 8, 11. The preheating chamber2 serves to receive and preheat the gas turbine blade 12. With theheating device 7 provided in the preheating chamber 2, the gas turbineblade 12 is heated from room temperature to a product temperature whichis the coating temperature.

The gas turbine blade 12 is pretreated in the preheating chamber 2 andprepared for subsequent method steps, in particular for the applicationof the metallic coating 13 to the gas turbine blade 12 in the coatingchamber 3. In the preheating chamber 2, possible impurities which mayhave entered the surface of the gas turbine blade 12 can also be emittedas gases from the gas turbine blade 12. Therefore the preheating chamber2, in addition to the preliminary process heating, at the same timeperforms an important cleaning function for the gas turbine blade 12 tobe coated.

After the heating and degassing process, a gas turbine blade 12 havingan appropriately clean prepared surface and well-defined producttemperature which is the coating temperature is prepared here. The gasturbine blade 12 is then automatically transferred by the transfersystem 8, 11 from the preheating chamber 2 into the coating region 9 ofthe coating chamber 3 and arranged on a movable holder 16, hererotatable about a longitudinal axis 17.

In the coating chamber 3, during the coating operation, a metalliccoating 13, for example an MCrAlX anti-oxidation coating, is applied tothe gas turbine blade 12. The coating material 15 (MCrAlX), for exampleby thermal spraying with VPS or LPPS spraying methods, is applied to thesurface of the gas turbine blade 12 moving about the longitudinal axis17, in this case rotating about the longitudinal axis 17.

In this case, the process time for applying this coating 13 is about 30min. During this period, the gas turbine blade 12 is held at a coatingtemperature of around 1100 K to about 1200 K by the process-related heatinput into the gas turbine blade 12. In this exemplary case, the gasturbine blade 12 is heated by the hot process gases of the coatingdevice 14 (plasma torch) and by the coating material 15 striking the gasturbine blade 12.

After the metallic coating 13 has been applied to the gas turbine blade12, the latter is automatically transferred by the transfer system 8, 11from the coating region 9 into the postheat treatment region 10. Thistransfer is effected via the lock chamber 4.

In the lock chamber 4, the gas turbine blade 12, by means of the heatingdevice 7 arranged there, is held at a predetermined product temperaturewhich is always higher than a minimum temperature. The minimumtemperature in this case is higher than room temperature and ispreferably 500 K, in particular between about 900 K and about 1400 K.

After the transfer, the gas turbine blade 12 provided with a metalliccoating 13 is subjected to a postheat treatment in the postheattreatment region 10, this postheat treatment taking place at a postheattreatment temperature of about 1200 K to 1500 K. To this end, the gasturbine blade 12 is brought to the predetermined postheat treatmenttemperature by means of the heating devices 7A and is held at thispostheat treatment temperature for a period of time. Here, the processtime is, for example, 120 min (also see descriptions with respect toFIG. 2 and FIG. 3). As a result, firm bonding (diffusion bonding)between the metallic coating 13 and the parent material of the gasturbine blade 12 is produced.

After the postheat treatment, the gas turbine blade 12 is automaticallytransferred from the postheat treatment chamber 5 into the coolingchamber 6. A gas turbine blade 12 is heated after it has been subjectedto the postheat treatment. In order to treat the gas turbine blade 12further or feed it to its destination, it is brought to room temperaturein a suitable manner. To this end, it has to be cooled down.

In conventional methods, this is likewise carried out in the externalpostheat treatment chamber, which does not have a vacuum coupling to thecoating chamber. In the vacuum plant, on the other hand, the controlledcooling operation is effected in the separate cooling chamber 6. Inorder to cool the gas turbine blade 12 in a controlled manner, a heatingdevice 7 is provided in the cooling chamber 6. This heating device 7ensures that the gas turbine blade 12 is at a predetermined temperatureduring the cooling operation. As a result, the gas turbine blade 12 isnot cooled too rapidly via heat radiation or heat conduction to thesurroundings, but is cooled virtually steadily by the temperature beingreduced down to room temperature gradually and in a controlled manner bycontrolling or regulating the heating output of the heating device 7.Once the gas turbine blade 12 has been cooled down to room temperaturein a controlled manner in the cooling chamber 6, it is removed from thecooling chamber 6.

The method, just described by way of example for a product 12, inparticular a gas turbine blade 12, for coating a product 12 with ametallic coating 13 is characterized by the fact that it is conceived asa continuous and simultaneous method. In this way, a plurality ofproducts 12 can pass through various method steps simultaneously andcontinuously. In FIG. 1, this is illustrated by the fact that, forexample, one gas turbine blade 12 is located in the coating region 9 andsimultaneously, a larger number of gas turbine blades 12 is in each caselocated in the preheating chamber 2, the lock chamber 4, the postheattreatment chamber 10 and the cooling chamber 6. A metallic coating 13 istherefore applied to gas turbine blades 12 in the coating region 9,while gas turbine blades 12 provided with a metallic coating 13 aresimultaneously subjected to a postheat treatment in the postheattreatment region 10; and at the same time gas turbine blades 12 arepretreated in the preheating chamber 2, and at the same time gas turbineblades 12 are cooled down in a controlled manner in the cooling chamber6, and at the same time gas turbine blades 12 are transferred in thelock chamber 4. A continuous and simultaneous pass of gas turbine blades12 through the various method steps is possible.

In particular, in this continuous method, the pass of gas turbine blades12 per unit of time is markedly increased compared with non-simultaneousand/or discontinuous methods. In the method, due to the differentprocess times of the individual method steps, more gas turbine blades 12are subjected to a postheat treatment than are coated at the same timein the coating region 9, since the postheat treatment process generallyconstitutes the limiting process with respect to time. By designing thevacuum plant 1 with due regard to the respective process times, acontinuous and simultaneous pass of products 12 is ensured, andefficient production of metallic coatings 13 on products 12 is madepossible. In this case, the method, in addition to the coating of gasturbine blades 12, is also suitable for coating other high-temperaturecomponents of a gas turbine, for example for heat shield elements of acombustion chamber.

In the following figures, the process control with regard to thetemperature profile according to a conventional method (FIG. 2) andaccording to the method according to the invention (FIG. 3) are comparedwith one another and explained in more detail. Reference is occasionallymade here to the reference numerals in FIG. 1 for the purpose ofclarification.

FIG. 2 shows a diagram in which the temperature is plotted against timefor a product 12, in particular for a gas turbine blade, according to aconventional coating method. The time t is plotted on the X-axis of thediagram, and the temperature T of the product 12 at a certain time tduring the method is plotted on the Y-axis. The product temperature T asa function of the time t is shown in the diagram as curve trace T₁(t).

The product 12 is first of all heated linearly from room temperatureT_(R) to a product temperature T which is the coating temperature T_(C).While the metallic coating 13 is being applied to the product 12, thetemperature for the coating process time Δt_(C) is kept at the coatingtemperature T_(C). The product 12 is then cooled down from the coatingtemperature T_(C) to room temperature T_(R).

The product 12 is then normally removed from the coating chamber 3, putinto intermediate storage in a suitable manner, and fed at anunspecified point in time to a postheat treatment chamber 5 for postheattreatment. The postheat treatment of the product 12 therefore does nottake place directly after the application of the metallic coating 13.

In order to illustrate this, the time axis t in FIG. 2 is interruptedafter the cooling to room temperature T_(R) and before the start of thepostheat treatment. This is therefore not a continuous method. Theproduct 12 is eventually subjected to a postheat treatment. To this end,the product 12 is first of all heated from room temperature T_(R)(linearly) to a product temperature T which is the postheat treatmenttemperature T_(H). The latter is higher than the coating temperatureT_(C). Since the postheat treatment generally has a longer process timethan the application of the metallic coating 13, the postheat treatmentprocess time Δt_(H) during which the product is at the postheattreatment temperature T_(H) is accordingly greater than the coatingprocess time Δt_(C).

For example, for a postheat treatment of products 12 which constitutegas turbine blades, the postheat treatment process time Δt_(H) is aboutfour times as great as the coating if process time Δt_(C). After thepostheat treatment, the product 12 is cooled down again from thepostheat treatment temperature T_(H) to room temperature T_(R). Theprocess control with regard to the temperature profile in a conventionalmethod is characterized by the fact that the product 12 is cooled downto room temperature T_(R) between the application of the metalliccoating 13 and the postheat treatment.

A diagram having a temperature profile for a product 12, in particularfor a gas turbine blade, according to the method according to theinvention is shown in FIG. 3. The time t is plotted on the X-axis of thediagram, whereas the product temperature T of the product 12 at acertain time t is plotted on the Y-axis of the diagram. The producttemperature T as a function of the time t is illustrated in the diagramby the corresponding curve trace T₂(t).

With this temperature profile, the product 12 is first of all heatedlinearly from room temperature T_(R) to a product temperature T which isthe coating temperature T_(c). While the metallic coating 13 is beingapplied to the product 12, the temperature for the coating process timeΔt_(C) is kept at the coating temperature T_(c). For products 12 whichconstitute, for example, gas turbine blades which are provided with anMCrAlX coating, the coating temperature T_(c) is 1100 K to about 1200 K.

Directly after the actual coating operation, the product 12 istransferred continuously from the coating region 9 into the postheattreatment region 10 through the lock chamber 4, which, as illustrated,is possibly associated with a change in the temperature of the product12, generally with a decrease in the temperature. The temperatureprofile in this method step is constructed in such a way that thepossible temperature decrease of the product 12 from the coatingtemperature T_(H) to a minimum temperature T_(min) is restricted, thisminimum temperature T_(min) being higher than room temperature T_(R). Ingas turbine blades, the minimum temperature T_(min) in this case ispreferably higher than 500 K, in particular between about 900 K and 1400K.

The product 12, for the postheat treatment, is then heated to a producttemperature T which is the postheat treatment temperature T_(H) andwhich, for example for gas turbine blades, in around 1200 K to 1500 K.The postheat treatment takes place at the postheat treatment temperatureT_(H), at which the product 12 is held for a postheat treatment processtime Δt_(H) is greater than the coating process time Δt_(C).

After the postheat treatment, the product 12 is cooled down from thepostheat treatment temperature T_(H) to room temperature T_(R). Thetime-dependent temperature profile of the product 12 according to thismethod has a continuous curve trace T₂(t) which, in particular, connectsthe plateau region having the coating temperature T_(C) and thefollowing plateau region having the postheat treatment temperature T_(H)in a controlled manner and continuously to one another. The connectionis effected in this case in such a way that, at all times, a minimumtemperature T_(min) of the product 12 is ensured, in which case theproduct 12 is definitely not cooled down to room temperature T_(R)and/or is definitely not exposed to the atmosphere.

This novel process control with regard to the temperature profile makesit possible to markedly improve the bonding of the metallic coating 13on the parent material of the product 12 during the postheat treatment.The product 12 in this case is always close to a state of thermodynamicequilibrium with its surroundings. Time and spatial temperaturegradients, in particular harmful thermal shocks as a result of coolingto room temperature T_(R), are avoided, which has a very advantageouseffect on the quality of the metallic coating.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A method of coating a product with a metallicanti-oxidation coating in one single vacuum plant, the plant including acoating chamber and a postheat treatment chamber separated from thecoating chamber, wherein the postheat treatment chamber is connected tothe coating chamber in a vacuum-tight manner, the method comprising:heating the product brought into the coating chamber and subjected to avacuum from room temperature to a product temperature; applying themetallic anti-oxidation coating to the product being in a vacuum;transferring the coated product from the coating chamber to the postheattreatment chamber by a transfer system without interruption of thevacuum; subjecting the coated product to a postheat treatment in thepostheat treatment chamber in a vacuum, wherein the postheat treatmentfollows the application of the coating in such a way that thetemperature of the product, after the application of the coating andbefore the postheat treatment, is at least equal to a minimumtemperature, the minimum temperature being higher than roomtemperatures; and transferring the coated product from the vacuum plant.2. The method as claimed in claim 1, wherein the minimum temperature isabout 500 K.
 3. The method as claimed in claim 1, wherein the product isautomatically transferred from the coating chamber into the postheattreatment chamber.
 4. The method as claimed in claim 1, furthercomprising: cooling down the product subjected to postheat treatment, toroom temperature in a controlled manner.
 5. The method as claimed inclaim 4, wherein the metallic anti-oxidation coating is an MCrAlX alloy,where M stands for one or more elements of the group including iron,cobalt and nickel; Cr stands for chromium; Al stands for aluminum; and Xstands for one or more elements of the group including yttrium, rheniumand the elements of the rare earths.
 6. The method as claimed in claim1, wherein a first number of products is located in the coating chamberand simultaneously, a second number of products is located in thepostheat treatment chamber, the second number being larger than thefirst number.
 7. The method as claimed in claim 1, wherein a materialused for the product is one of a nickel-, iron-, or cobalt-basesuperalloy.
 8. The method as claimed in claim 7, wherein the metallicanti-oxidation coating is an MCrAlX alloy, where M stands for one ormore elements of the group including iron, cobalt and nickel; Cr standsfor chromium; Al stands for aluminum; and X stands for one or moreelements of the group including yttrium, rhenium and the elements of therare earths.
 9. The method as claimed in claim 1, wherein the metallicanti-oxidation coating is an MCrAlX alloy, where M stands for one ormore elements of the group including iron, cobalt and nickel; Cr standsfor chromium; Al stands for aluminum; and X stands for one or moreelements of the group including yttrium, rhenium and the elements of therare earths.
 10. The method of claim 1, wherein the minimum temperatureranges from about 900 K to about 1400 K.
 11. A method of coating aproduct with a metallic anti-oxidation coating in one single vacuumplant, the plant including a coating chamber, a postheat treatmentchamber, and a lock chamber connecting the coating chamber and thepostheat treatment chamber, the method comprising: heating the product,brought into the coating chamber and subjected to a vacuum, from roomtemperature to a product temperature; applying the metallicanti-oxidation coating to the product; transferring the coated productfrom the coating chamber to the lock chamber by a transfer system,wherein a temperature of the product, after coating and before postheattreatment, is at least equal to a minimum temperature which is higherthan room temperature; transferring the coated product from the lockchamber to the postheat treatment chamber by a transfer system;subjecting the coated product to a postheat treatment being in a vacuum;and transferring the coated product from the vacuum plant.
 12. A methodof coating a product with a metallic anti-oxidation coating in onesingle vacuum plant having a coating chamber and a postheat treatmentchamber separated from the coating chamber, wherein the postheattreatment chamber is connected to the coating chamber in a vacuum-tightmanner, the method comprising: heating the product brought into thecoating chamber and subjected to a vacuum from room temperature to aproduct temperature and applying the metallic anti-oxidation coating tothe product being in a vacuum; transferring the coated product from thecoating chamber to a postheat treatment chamber by a transfer systemwithout interruption of the vacuum; subjecting the coated product to apostheat treatment in the postheat treatment chamber in a vacuum, usinga heating device, enabling a different temperature compared to thetemperature of the coating chamber, wherein the postheat treatmentfollows the application of the coating in such a way that thetemperature of the product, after the application of the coating andbefore the postheat treatment, is at least equal to a minimumtemperature, the minimum temperature being higher than room temperature;and transferring the coated product from the vacuum plant.
 13. A methodof coating a product with a metallic anti-oxidation coating in onesingle vacuum plant, the plant including a coating chamber and apostheat treatment chamber separated from the coating chamber, whereinthe postheat treatment chamber is connected to the coating chamber in avacuum-tight manner, the method comprising: heating the product broughtinto the coating chamber and subjected to a vacuum from room temperatureto a product temperature and applying the metallic anti-oxidationcoating to the product being in a vacuum; transferring the coatedproduct from the coating chamber to the postheat treatment chamber by atransfer system without interruption of the vacuum; subjecting thecoated product to a postheat treatment in the postheat treatment chamberin a vacuum and simultaneously heating and coating a new number ofproducts in the coating chamber, wherein the postheat treatment followsthe application of the coating in such a way that the temperature of theproduct, after the application of the coating and before the postheattreatment, is at least equal to a minimum temperature, the minimumtemperature being higher than room temperature; and transferring thecoated product from the vacuum plant.
 14. An apparatus for coating aproduct with a metallic anti-oxidation coating in one single vacuumplant, comprising: a coating chamber; a postheat treatment chamberseparated from the coating chamber, wherein the postheat treatmentchamber is connected to the coating chamber in a vacuum-tight manner,wherein both chambers are maintained in vacuum such that the product isnot exposed to the atmosphere from a time of entry into the vacuum plantuntil a time of exit from the vacuum plant, and wherein the postheattreatment chamber is connected to the coating chamber such that theproduct is transferable by a transfer system from the coating chamber tothe postheat treatment chamber without interruption of the vacuum. 15.The apparatus as claimed in claim 14, wherein a heating device isprovided in the postheat treatment chamber.
 16. The apparatus as claimedin claim 14, further comprising: a preheating chamber, the preheatingchamber being arranged upstream of the coating chamber and beingconnected to the coating chamber in a vacuum-tight manner.
 17. Theapparatus as claimed in claim 16, further comprising: a cooling chamber,the cooling chamber being arranged downstream of the postheat treatmentchamber and being connected to the postheat treatment chamber in avacuum-tight manner.
 18. The apparatus as claimed in claim 16, whereinthe vacuum-tight connection between the coating chamber and the postheattreatment chamber is produced via a lock chamber.
 19. The apparatus asclaimed in claim 18, wherein a heating device is provided in the lockchamber.
 20. The apparatus as claimed in claim 16, wherein thevacuum-tight connection between the coating chamber and the preheatingchamber is produced via a lock chamber.
 21. The apparatus as claimed inclaim 20, wherein a heating device is provided in the lock chamber. 22.The apparatus as claimed in claim 14, further comprising: a coolingchamber, the cooling chamber being arranged downstream of the postheattreatment chamber and being connected to the postheat treatment chamberin a vacuum-tight manner.
 23. The apparatus as claimed in claim 22,wherein the vacuum-tight connection between the coating chamber and thepostheat treatment chamber is produced via a lock chamber.
 24. Theapparatus as claimed in claim 23, wherein a heating device is providedin the lock chamber.
 25. The apparatus as claimed in claim 14, whereinthe connection between the coating chamber and the postheat treatmentchamber is produced via a lock chamber.
 26. The apparatus as claimed inclaim 25, wherein a heating device is provided in the lock chamber. 27.The apparatus as claimed in claim 14, further comprising: a transfersystem for the automatic transfer of the product from one chamber intoanother chamber of the vacuum plant.
 28. The apparatus as claimed inclaim 14, wherein the coating chamber includes a first receivingcapacity for products and the postheat treatment chamber includes asecond receiving capacity for products, the second receiving capacitybeing greater than the first receiving capacity.
 29. A vacuum plant,comprising: a coating chamber, wherein a product is adapted to be coatedwith a metallic anti-oxidation coating while in a vacuum; a postheattreatment chamber, wherein the coated product is adapted to be subjectedto postheat treatment while in a vacuum; a lock chamber, which producesa vacuum-tight connection between the coating chamber and the postheattreatment chamber, wherein the lock chamber separates the postheattreatment chamber from the coating chamber, and wherein a temperature ofthe product after coating and before postheat treatment is at leastequal to a minimum temperature which is higher than room temperature;and a plurality of transfer systems respectively provided in each of thecoating chamber, the postheat treatment chamber, and the lock chamber,which transfers the product from one chamber to another withoutinterruption of the vacuum.
 30. The vacuum plant of claim 29, whereinthe minimum temperature is about 500 K.
 31. The vacuum plant of claim29, wherein the minimum temperature ranges from about 900K to about 1400K.
 32. The vacuum plant of claim 29, further comprising: a preheatingchamber, the preheating chamber being arranged upstream of the coatingchamber and being connected to the coating chamber in a vacuum-tightmanner.
 33. The vacuum plant of claim 32, further comprising: a coolingchamber, the cooling chamber being arranged downstream of the postheattreatment chamber and being connected to the postheat treatment chamberin a vacuum-tight manner.
 34. The vacuum plant of claim 32, wherein thetransfer systems automatically transfer the product from one chamberinto another chamber of the vacuum plant.
 35. The vacuum plant of claim29, further comprising: a cooling chamber, the cooling chamber beingarranged downstream of the postheat treatment chamber and beingconnected to the postheat treatment chamber in a vacuum-tight manner.36. The vacuum plant of claim 35, wherein the transfer systemsautomatically transfer of the product from one chamber into anotherchamber of the vacuum plant.
 37. The vacuum plant of claim 29, whereinthe transfer systems automatically transfer the product from one chamberinto another chamber of the vacuum plant.
 38. A vacuum plant,comprising: a coating chamber, wherein a product is adapted to be coatedwith a metallic anti-oxidation coating while in a vacuum; a postheattreatment chamber with a second heating device, wherein the coatedproduct is adapted to be subjected to heat treatment while in a vacuum;wherein the postheat treatment chamber is separated from the coatingchamber through a lock chamber with a first heating device; wherein thefirst heating device is separately controllable from the second heatingdevice; wherein the lock chamber produces a vacuum-tight connectionbetween the coating chamber and the postheat treatment chamber; whereina temperature of the product after coating and before postheat treatmentis at least equal to a minimum temperature which is higher than roomtemperature; and a plurality of transfer systems respectively providedin each of the coating chamber, the postheat treatment chamber, and thelock chamber, which transfers the product from one chamber to anotherwithout interruption of the vacuum.